Generally known valve operating means for use in rotary valves include, for example, worm gearing which is employed to prevent the rotation of the valve stem and the resulting displacement of the valve disk due to the fluid pressure acting on the valve disk or the negative pressure produced downstream of the valve disk when the valve disk controls a flow of fluid. The valve disk which is subject to fluid pressure is made operable with a small force by the worm gearing, utilizing its reduction ratio.
In order to render the valve disk operable with a small force, the worm gearing must have a large reduction ratio, which entails the necessity of greatly increasing the diameter of the worm wheel and consequently enlarges the valve itself. Moreover, because the worm wheel meshes with the worm having an axis at right angles to the axis of rotation of the worm wheel, the rotary shaft portion of the worm projects from the worm wheel. Thus the worm gearing has the disadvantage of making the valve construction still larger.
Especially when the rotary valve is mounted on an underground pipe with the rotatable stem of its valve disk positioned in a perpendicular direction, the operating worm which is at right angles to the axis of the rotatable stem is in a horizontal position. Accordingly, if it is attempted to drive the worm from above, there arises the need to form a fairly large vault in the ground for the operation of the valve. Otherwise, it would become necessary to employ additional members such as bevel gears for turning the direction of operation upward and therefore to provide a large space for accommodating the bevel gears or like means. Conversely, even when the valve is mounted on an underground pipe in such a position that the axis of rotation of the valve disk is horizontal, a portion of the rotatable valve stem fixed to the valve disk must be made to project from the valve case to render the valve disk rotatable from outside, so that the projection of the stem, worm wheel and worm require a correspondingly enlarged space on the lateral side of the valve case. In either case, therefore, the worm gearing has the drawback of necessitating a considerably large underground space for operation.
In place of worm gearing, lever or link means is usable, but the lever or link structure makes the valve itself large and requires an additional space for allowing the pivotal movement of link or lever means, which leads to the need for a still larger space for operation. Such means further involves the inconvenience of being unable to automatically maintain the valve in its set position when the valve disk is subjected to a torque due to fluid pressure or the like, unless it incorporates a special lock mechanism.